<template>
<ul class="aphabet">
	<li class="item" v-for="(item,key) of cities" 
	@click="handleItemClick"
	@touchstart.prevent="handleTouchStart"
	@touchmove="handleTouchMove"
	@touchend="handleTouchEnd"
	:key="key"
	:ref="key"
	>{{key}}
	</li>
</ul>
</template>

<script>
export default {
	name: 'CityAphabet',
	props: {
		cities: Object
	},
	computed: {
		letters () {
			const letters = []
			for (let i in this.cities) {
				letters.push(i)
			}
			return letters
		}
	},
	data () {
		return {
			touchStatus: false,
			startY: 0,
			timer: null
		}
	},
	updated () {
		this.startY = this.$refs['A'][0].offsetTop
	},
	methods: {
		handleItemClick (e) {
			this.$emit('change', e.target.innerText)
		},
		handleTouchStart () {
		  this.touchStatus = true
		},
		handleTouchMove (e) {
			if (this.touchStatus) {
				if (this.timer) {
					clearTimeout(this.timer)
				}
				this.timer = setTimeout(() => {
					const touchY = e.touches[0].clientY - 79
					const index = Math.floor((touchY - this.startY) / 20)
					if (index >= 0 && index < this.letters.length) {
						this.$emit('change', this.letters[index])
					}
				}, 16)
			}
		},
		handleTouchEnd () {
			this.touchStatus = false
		}
		
	}
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.aphabet
	display: flex
	flex-direction: column
	justify-content: center
	position: absolute
	top: 1.58rem
	right: 0rem
	bottom: 0rem
	width: .4rem
	.item
		line-height: .4rem
		text-align: center
		color: $bgColor
</style>
